1. Field of the Invention
The present invention relates to bonding of optical elements such as an optical waveguide, an optical collimator, an optical attenuator, an optical isolator, etc., and in particular, to an apparatus and method for bonding the optical elements by non-contact soldering.
2. Description of the Related Art
There are several known methods of soldering electronic devices and optical elements. A first method is to heat a portion to be bonded by means of an electric iron and then supply lead. A second method is to place a high-frequency induction heater around the optical elements and apply constant heat to the portion to be bonded by high-frequency heating. A third method is to perform soldering by using a laser light source as a heat source, which is available where the electric iron cannot be used due to the high packaging density or there is mass production due to many portions to be bonded, as shown, for example, in U.S. Pat. No. 4,963,714 to Joseph R. Adamski et al. entitled Diode Laser Soldering System. Lastly, a fourth method, which is available where there are many different portions to be bonded, is to apply heat to the portions to bonded by changing a light path using a prism. Here, the lead used in the first and second methods is in the form of a wire. The third and fourth methods, however, utilize lead powder plastered around the portions to be bonded.
The soldering processes according to the known methods are frequently applied to electronic devices. However, in order to apply such a soldering process to optical devices, the following should be considered:
(1) A possible contact during application of the heat to the bonding portions may affect the alignment of the optical elements; PA1 (2) Bonding portions of the optical elements should be kept symmetric to prevent misalignment of the optical elements due to thermal expansion; PA1 (3) Heat should be uniformly applied to symmetrical bonding portions to prevent misalignment of the optical elements; PA1 (4) The bonding portions should be filled completely with lead to secure reliability of the optical elements; and PA1 (5) Reproducibility and mass production of the optical elements should be guaranteed.
My examination of weak points in connection with the respective soldering methods mentioned above based on the foregoing considerations shows that neither the first nor second soldering methods meet all of the foregoing five points of consideration. Regarding the third soldering method, while meeting symmetry of optical elements arranged in a plane, it does not meet the foregoing considerations as to symmetry in three-dimensional space. Regarding the forth soldering method, while making connection of desired portions possible, it cannot secure the symmetry.
In short, though very useful to the electronic devices, the conventional soldering methods are not suitable for optical elements due to the misalignment problem. That is to say, during application of heat to the bonding portions, if the lead contacts the surface of the bonding portions, the optical elements may be misaligned. Further, the laser beam applied to the bonding portions of the optical elements cannot be kept symmetric, which causes the misalignment of the optical elements due to the thermal expansion and non-uniform distribution of heat. As a result, the properties of the optical elements are affected, thus lowering reliability of the products. In addition, the reproducibility and mass production of the optical elements are also lowered.